1. Field of the Invention
An object of the present invention is a device for fitting out or equipping a hole in a panel, especially an aircraft panel, although it can also be used in any other type of structure. It also pertains to a panel thus equipped. The invention seeks to help improve the performance of the panels provided with such holes, whether these holes are made because of an a priori requirement or because of subsequent repairs to the panel.
For the building of structures, especially aircraft, it is the common practice to make panels which are typically panels for the wings and fuselage of an aircraft. For reasons of weight and mechanical hardness, the panels are generally made out of composite materials, typically sheets of carbon fiber and/or sheets of stratified material. In the structure into which this panel is fitted, the panel causes the volumes on one side of the panel to be separated from those located on the other side. It is sometimes necessary to transmit information, or fluids, from one side to the other. It then becomes necessary to make a hole in the panel to enable this passage. In other situations, the panel will have been damaged at a particular place and the deterioration of the material of the panel at this place requires the making of a clean hole, and the fitting out of this hole with a repairing part. In other cases, the hole is simply designed to enable an inspection, in which case it is permanently plugged with a lid that is removed during inspection.
The problem presented by composite materials, especially those working under compression in the direction of the plane of the panel, is that the making of a hole unacceptably burdens the corresponding resistance. In practice, the breaking of such a panel under extreme compression (which is itself far greater than the limit of compression that the panel should undergo during use, especially during flight, as dictated by the JAR and FAR safety coefficients) takes the form of a delamination in the thickness of the panel, and an interpenetration of two parts of this panel subjected to stress at the position of this delamination.
This interpenetration, which is synonymous with breakage, takes place when a hole is made in the panel. It occurs on the one hand approximately facing a diameter of the hole which is perpendicular to the direction of the compression, and on the other hand at a compression value that is very appreciably lower than a borderline value obtained when there is no hole present. In one example, the ratios of these values are about 2 or 3. The weakening caused by the presence of a hole is measured accordingly.
2. Background of the Invention
To overcome this type of problem, there is a known way of reinforcing the panel at the position where the hole is made. It would seem however that this reinforcement entails a complicated operation, especially when stiffeners (separated from one another in practice by a gap of about 20 centimeters) are present at the position of the reinforcement. Besides, once this reinforcement is made, the equipping of the hole, especially in order to place a lid, will itself normally weaken the edges of the hole and therefore contribute to reducing the efficiency of the reinforcement made. In any case, the equipment, especially owing to the presence of the stiffeners, leads to considerable excess weight, especially in the case of aircraft. In a practical example, the holes may have dimensions ranging from some centimeters to 20 centimeters.